Ivermectin paste is a 1.87% oral anthelmintic gel formulated exclusively for equine veterinary use, calibrated via a mechanical syringe plunger with locking ring notches where each individual notch delivers 91 mcg/lb (200 mcg/kg) for 250 lbs (113 kg) of equine body weight to treat strongyles, pinworms, and stomach bots in horses.
Equine deworming protocols require accurate calculation of horse body weight to ensure effective parasite clearance and prevent the emergence of anthelmintic-resistant nematodes. Misunderstanding syringe calibrations or attempting to use concentrated livestock pastes across different species leads to treatment failures or fatal toxicosis.
Equine Weight-to-Notch Calibration Reference Table
Standard 1.87% equine ivermectin paste syringes contain 6.08 grams of paste (113.7 mg of active ivermectin), capable of treating a 1,250 lb (567 kg) horse at the standard 200 mcg/kg rate.
| Equine Body Weight (lbs) | Equine Body Weight (kg) | Syringe Locking Ring Setting | Active Ivermectin Delivered (mg) |
|---|---|---|---|
| 250 lbs | 113 kg | 1st Notch (250 lb mark) | 22.7 mg |
| 500 lbs | 227 kg | 2nd Notch (500 lb mark) | 45.5 mg |
| 750 lbs | 340 kg | 3rd Notch (750 lb mark) | 68.2 mg |
| 1,000 lbs | 454 kg | 4th Notch (1,000 lb mark) | 91.0 mg |
| 1,250 lbs | 567 kg | Full Syringe (1,250 lb mark) | 113.7 mg |
| 1,500 lbs | 680 kg | 1 Full Syringe + 250 lb Notch | 136.4 mg |
Correct Administration Technique for Horses
To ensure full ingestion and avoid paste ejection, equine caretakers follow standard oral administration technique:
- Accurately Estimate Horse Weight: Use an equine weight tape placed snugly around the heart girth directly behind the withers, or weigh on a livestock platform scale.
- Set the Syringe Locking Ring: Turn the serrated ring on the plunger shaft until the side nearest the barrel aligns precisely with the horse’s weight mark. Lock the ring firmly.
- Ensure Mouth is Free of Feed: Inspect the horse’s mouth to ensure it is clear of hay, grain, or grass, which can cause the horse to spit out the paste.
- Administer on the Back of the Tongue: Insert the syringe nozzle through the interdental space (bars of the mouth) and depress the plunger onto the base of the tongue. Immediately elevate the horse’s head for a few seconds to encourage swallowing.
Major Equine Parasites Cleared by Ivermectin Paste
Oral 1.87% paste provides comprehensive broad-spectrum activity against equine internal parasites:
- Large Strongyles (Strongylus vulgaris): Destructive bloodworms whose migrating larvae cause verminous arteritis and fatal thromboembolic colic in horses.
- Small Strongyles (Cyathostomins): Encysted larvae in the cecal and colonic mucosa causing severe weight loss, unthriftiness, and larval cyathostominosis upon synchronous emergence.
- Equine Pinworms (Oxyuris equi): Inhabit the large colon and lay eggs on perianal skin, causing intense tail rubbing and hair loss.
- Stomach Bots (Gasterophilus species): Oral and gastric larvae of bot flies that attach to the stomach lining, causing ulcers and gastric irritation.
- Neck Threadworms (Onchocerca cervicalis microfilariae): Cause cutaneous onchocerciasis and ventral midline dermatitis in horses.
Why Horse Paste Must Never Be Used by Humans or Small Pets
Toxicology centers and the FDA issue strong warnings against human or small pet consumption of livestock paste:
- Extreme Overdose Potential: A single 250 lb notch delivers nearly 23 mg of drug—far above the human single dose of 12–15 mg for an adult—and can prove instantly lethal to dogs and cats.
- Non-Pharmaceutical Excipients: Industrial emulsifiers, artificial apple flavorings, and chemical stabilizers in horse pastes can induce severe gastric mucosal inflammation and chemical gastritis in humans.
- Lack of Human Bioavailability Testing: Veterinary gel vehicles alter gastrointestinal absorption unpredictably, leading to sudden dangerous spikes in plasma drug concentration.
Equine Parasite Refugia & Sustainable Strategic Deworming Protocols
Modern equine veterinary medicine emphasizes the preservation of ‘refugia’—the population of parasites that have not been exposed to anthelmintics and therefore retain genetic susceptibility to treatment. Indiscriminate rotational deworming every 8 weeks has driven widespread resistance in small strongyles and ascarids across horse stables worldwide.
Equine practitioners recommend performing semi-annual Fecal Egg Count (FEC) tests before administering ivermectin paste. Horses are classified as low egg shedders (<200 eggs/gram), moderate shedders (200–500 EPG), or high shedders (>500 EPG). Low shedders require only 1 to 2 targeted treatments per year (typically in spring and autumn), reducing environmental drug selection pressure while maintaining herd health.
Frequently Asked Questions (FAQ)
Can you give ivermectin horse paste to dogs?
No. Horse paste is highly concentrated and dangerous for dogs. Small measurement errors deliver massive toxic overdoses, causing blindness, seizures, coma, and death, especially in herding breeds with the MDR1 mutation.
How often should horses be dewormed with ivermectin paste?
Modern equine parasitology recommends targeted strategic deworming based on spring and autumn Fecal Egg Counts (FEC), rather than rotational interval deworming, to prevent anthelmintic resistance.
Can pregnant mares receive ivermectin paste?
Yes. FDA-approved 1.87% equine ivermectin paste has been evaluated as safe for pregnant mares, breeding stallions, and foals over 6 to 8 weeks of age.
What should I do if my horse spits out half the paste?
Do not immediately re-administer a full dose. Consult your equine veterinarian to determine whether a partial booster is appropriate based on the estimated amount lost.
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